Anti-resonant HCF light guidance relies on inhibited coupling between core and cladding modes and anti-resonance effects at the core/cladding interface. Various types of antiresonant HCFs have been proposed, including Kagome fibers, negative curvature fibers and non-touching capillary fibers. In these fibers, the thickness of the core/cladding interface is designed to be in antiresonance at the wavelength of operation such that the electromagnetic field is pushed into the hollow-core. The antiresonant glass membrane is very effective at repelling light away from the cladding. Therefore, surface scattering loss and damage threshold are significantly improved. However, confinement losses and bend sensitivity limit their maximum transmittable power.
Anderson localization is the absence of diffusive transport of waves in a highly disordered medium. In order to observe Anderson localization, the disorder must be strong enough that the wave scattering transport length l* becomes of the order of the wavelength, i.e., kl*˜1, where k is the effective wave vector in the medium. While it can be difficult to satisfy this condition and observe strong localization effects for light in three dimensions, the required conditions are relaxed in two-dimensional systems. Two-dimensional disordered systems are always localized, and the localization length ξ, which is the effective width of the localized beam, is related to l* by ξ=l*exp(τkTl*/2). If the randomness in the refractive index profile is only limited to the transverse plane of an optical wave, the effective transverse component of the wave vector kT is 10-100 times smaller than k; therefore, even small disorder (i.e., large l*) can result in a beam diameter that is smaller than the transverse dimensions of the system.
A hollow core optical fiber guides light within a hollow region where only a very small portion of optical power propagates inside the solid fiber material, which is typically made of glass. This helps to minimize nonlinear effects and provides a significantly higher damage threshold. Light guiding within a hollow core is not possible with conventional optical fiber designs which work based on total internal reflection. However, a different guiding mechanism can be used, based on a photonic bandgap, as can be realized in a photonic crystal fiber with a certain structure.
What is needed is an improved optical fiber that addresses the above-noted issues.